During the past 12 years my laboratory has been concerned with proximate mechanism underlying the synthesis of a pheromone that appears in the feces of maternally-behaving rats. Now that we have identified many of these mechanisms and can characterize the pheromone in general molecular terms, we shall ask why preweanling young approach the pheromone and consume pheromone-containing feces. We think that in doing so they gain two advantages, one relating to the gut and the other to the brain. Our hypothesis is that "pheromone feces" are rich in deoxycholic acid and that the ingestion of this secondary bile acid guards the pup against enteric infection and promotes the absorption of long-chain fatty acids for use centrally in myelination. The methodology we shall employ is that of Biopsychology and Biochemistry. If the experiments we intend to carry out prove successful, then we will have increased our understanding not only of gut maturation but of brain maturation as well. This in turn may offer clues for the treatment of selected enteric and dysmyelinating diseases.